Shed-forming device

ABSTRACT

The disclosure concerns a shed-forming device including a jacquard device in which the heddles, are connected to a pull-back element, for exerting a downward force on the heddle, wherein for each heddle, a yarn tensioning element is provided to change the yarn tension in at least one associated warp thread, and where a control or steering unit is provided for steering or controlling the yarn tension in at least one associated warp thread, separately for each heddle, in order to bring the total downward force on the heddle to a specific value or vary this according to a specific profile.

FIELD OF THE DISCLOSURE

The disclosure concerns a shed-forming device comprising a jacquarddevice with a number of heddles for positioning at least one associatedwarp thread, wherein each heddle is connected to a pull-back element forexerting a downward force on the heddle.

BACKGROUND

During successive weft insertion cycles on a weaving machine, one ormore weft threads are inserted into a shed formed between the warpthreads. In order to weave according to a predefined weaving pattern,the various warp threads must be correctly positioned in each shedrelative to one or more levels at which weft threads are inserted. Ajacquard machine is used for positioning several warp threadsdifferently in each shed.

Positioning takes place by means of heddles which are connected torespective hooks via cords, wherein each heddle has a heddle eye. Thehooks can be moved up and down by means of upwardly and downwardlymoving knives, and selected by selection means so as to be held or notheld in one of a number of possible positions. Each warp thread extendsthrough a heddle eye of a heddle, so that each different position of theheddle corresponds to a different position of the warp thread.

To allow the shed formation to take place correctly and to facilitatethe downward movement of the hooks, each heddle is connected to apull-back spring which is provided for exerting a downward force on theheddle. In the lowest position of a heddle, the extension of the springis at its smallest, so that the downward force exerted by this pull-backspring on the heddle is then at a minimum. The pull-back spring isselected such that this minimum force is still just sufficient to allowthe hook connected to the heddle to engage correctly on a selection edgeof a knife.

In the lowest position of the heddle, the warp threads which extendthrough the heddle eye also exert an upward force on the heddle. This isthe result of the yarn tension in these warp threads. In this lowestposition, the pull-back spring must therefore exert a downward force onthe heddle which is greater than said upward force, and the resultingdownward force must also be just sufficient to allow the selection hookto engage on a selection edge of a knife. Consequently, this minimumdownward tensile force may not be too small.

When the heddle is moved to a higher position by the knife, the downwardspring force increases proportionally with the upward movement of theheddle, so as to finally reach a value which is much greater thannecessary. As a result, the mean tension on the warp threads is muchhigher than necessary. A higher tension means more wear on machinecomponents, more extensive and more frequent damage to the warp threadsthemselves, and more energy consumption of the machine.

SUMMARY

The object of this disclosure is to remedy these disadvantages.

This object is achieved by providing a shed-forming device with thefeatures specified in the first paragraph of this description, whereinaccording to this disclosure, the shed-forming device comprises, perheddle, a yarn tensioning element which is provided to change the yarntension in at least one associated warp thread, and the shed-formingdevice comprises a control or steering unit which is provided, incooperation with the respective yarn tensioning elements, for steeringor controlling the yarn tension in at least one associated warp threadseparately for each heddle, such that the total downward force on theheddle is brought to a specific value or varies according to a specificprofile.

The tension profile in the warp yarn can be steered or controlled bymeans of a shed-forming device according to this disclosure such that atall times, the combined effect of the yarn tension and the spring exertsa downward force on the heddles which is sufficiently large to achieve agood shed formation but reaches lower top values than with existingshed-forming devices. This means less wear, less yarn damage and a lowerenergy consumption.

In addition, pull-back elements may be selected which are not aspowerful. In the lowest heddle position, the yarn tension can still besteered or controlled to a lower value than with the existingshed-forming device. The pull-back element must then provide a lowerforce in order to achieve the minimum required downward force.

The steering or control system may also be designed to allow the totaldownward force during the weaving process to take a number of successivevalues which are predefined. In some cases also certain machineparameters, such as machine position or machine speed, or data connectedwith the weaving pattern or weave structure, may be made available tothe steering or control system in order to be taken into account indetermining the target value for the total downward force.

Said profile may be selected for example from a collection of two ormore reference profiles or two or more reference series, such as e.g.tables or files, with at least one reference value for the yarn tension.During weaving then, for example on the basis of machine parametersand/or weaving pattern data, a suitable reference profile or referenceseries may be selected.

In a preferred embodiment, each yarn tensioning element comprises aroller which is driven by a motor and is in contact with at least onewarp thread, and is intended to rotate in the one or the other directionof rotation in order to move said warp thread in a direction oppositethe feed direction of the warp threads, or to move the warp thread or tofacilitate the movement thereof, so as to move with the movement thereof(i.e. a moving warp thread) in a direction which is the same as the feeddirection of the warp threads, in order to increase or decreaserespectively the yarn tension in said warp thread.

The pull-back elements may be any type of element which is designed toexert a force, such as amongst other elements in which the force issupplied at least partially by a pneumatically driven element and/or byforce of gravity. Preferably, these are elements in which the downwardforce is supplied at least partially, and preferably exclusively ormainly, by an elastically deformable element. In a most preferredembodiment, the pull-back elements are springs.

The yarn tensioning device preferably comprises measuring means inorder, in at least one warp thread or in several (at least two) warpthreads which form a part group, to measure the yarn tension or avariable which is a measure of the yarn tension. Preferably, a steeringunit is also provided with means for repeatedly or continuouslycomparing the measured yarn tension, or the variable which is a measureof the yarn tension, with a reference value, and when a difference isestablished between the measured yarn tension or variable on the onehand and the reference value on the other, generating a control signalfor driving a yarn tensioning element (e.g. by adapting the current withwhich the motor is controlled or by adapting the motor torque) such thatthe difference between the measured value and the reference value isreduced.

A control unit preferably comprises a regulator which is provided, onsetting a specific target value for the yarn tension, to generate acontrol signal for driving a yarn tensioning element (e.g. by adaptingthe current with which the motor is controlled or by adapting the motortorque) such that the target value is approached or reached. Theregulator is preferably a regulator of the type with “feed-forwardcontrol”.

In a particular embodiment of a steering or control unit, machineparameters may also be made available, such as the machine position ormachine speed, or data connected with the weaving pattern or weavestructure, and one or more of these parameters may be used for controlor steering.

If one or more yarn tension influencing circumstances differ fordifferent part groups of warp threads, then in this weaving machinedifferent reference yarn tension profiles may be determined for thesepart groups, and these reference yarn tension profiles may be adaptedseparately and if necessary differently in the different part groupsduring the weaving process, according to circumstances which havechanged during the weaving process. The yarn tension may thereby onaverage be kept slightly lower while the maximum values of the yarntension are not as high.

The yarn tensioning device comprises for example detection means fordetecting the status of one or more yarn tension influencingcircumstances during weaving, and/or comprises storage means and/ordata-processing means in order to predefine the time or phase of theweaving process at which the yarn tension influencing circumstanceoccurs, for example on the basis of the weaving pattern and/or on thebasis of the proposed path of warp threads between the yarn store andthe fabric.

Preferably, in this weaving machine and according to the method of thisdisclosure, a control system is applied using a “bidirectional forcedfeed-forward function”. This means that, on a change of movement of theyarn, the yarn tensioning unit intervenes to facilitate this change soas to react more quickly.

Further particular features of this shed-forming device are described inthe claims.

The disclosure is now explained further with reference to thedescription which follows of a possible embodiment of a jacquard machineaccording to this disclosure. It is emphasised that the device andmethod described are merely examples of the general principle of thedisclosure, and thus may in no way be regarded as a limitation of thescope of protection specified in the claims or of the area ofapplication of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

In this description, reference signs are used to refer to the attachedfigures, in which:

FIG. 1 is a diagrammatic side view of a structure of a weaving machineand a bobbin creel with associated yarn tensioning device;

FIG. 2 is a graph showing the following for a pile-forming pile warpthread in a number of successive weft insertion cycles during weaving,according to the prior art:

-   -   the development of the position of the heddle eye (in mm),    -   the development of the upward or downward component of the force        (in N) which is exerted on the heddle as a result of the yarn        tension in the pile-forming pile warp thread,    -   the development of the downward spring force exerted by the        pull-back spring on the heddle of the pile warp thread (in N),        and    -   the development of the sum of the downward spring force (in N)        on the heddle and the upward or downward component of the force        (in N) which is exerted on the heddle as a result of the yarn        tension in the pile-forming pile warp thread.

FIG. 3 is a graph showing the following for a pile-forming pile warpthread in a number of successive weft insertion cycles during weavingwith a controlled or steered yarn tension according to the disclosure:

-   -   the development of the position of the heddle eye (in mm),    -   the development of the upward or downward component of the force        (in

N) which is exerted on the heddle as a result of the yarn tension in thepile-forming pile warp thread,

-   -   the development of the downward spring force exerted by the        pull-back spring on the heddle of the pile warp thread (in N),    -   the development of the sum of the downward spring force (in N)        on the heddle and the upward or downward component of the force        (in N) which is exerted on the heddle as a result of the yarn        tension in the pile-forming pile warp thread, and    -   the mean of said sum of forces.

DETAILED DESCRIPTION

In a particular installation, a weaving machine (1) in cooperation witha jacquard device (2) is installed next to a bobbin creel (3), and abeam stand (4) with four rollers (40)-(43) each containing a yarn storeis arranged in the space between the weaving machine (1) and the bobbincreel (3).

A yarn tensioning device (6) is installed in the space between thebobbin creel (3) and the weaving machine (1), and consists of a yarntensioning module (20) which extends in the horizontal directionparallel to a vertical plane containing the front sides (30a) of theplurality of mutually adjacent creel units (30). The yarn tensioningmodule (20) consists of two panel-like carriers (21), (22) with a flatouter surface, which run symmetrically relative to a horizontal planetowards each other in the direction of the weaving machine (1), whereinthey converge and join together at an angle. The yarn tensioning module(20) has a V-shaped profile viewed in a vertical cross-section. Eachcarrier (21), (22) carries a large number of rows of yarn tensioningelements (8) placed closely adjacent to each other. For reasons ofclarity, only three yarn tensioning elements (8) are shown for eachcarrier (21), (22). For each warp thread which is guided from arespective bobbin in the bobbin creel (3) to the weaving machine (1), aguide tube (10) is provided for guiding the warp thread without tensionto a respective yarn tensioning element (8).

The warp threads are moved further from the yarn tensioning elements (8)to a grid (100) with the same width as the yarn tensioning module (20)but with a smaller height. From the grid (100), the warp threads (11),(12) run to the weaving machine (1) where they pass through the heddleeye of a respective heddle (16), (17), shown symbolically by a verticalline with a circular widening which depicts the heddle eye. A respectivepull-back spring (18), (19) exerts a downward force on each heddle (16),(17).

According to the prior art, the warp threads are supplied in stretchedstate from the bobbin creel (3) to a first grid (X). FIG. 1 shows thesituation of the prior art with the straight line (S1) which runs fromthe top row of bobbins in the bobbin creel (3) firstly through the grid(X) of an existing installation and then on to the grid (100), and thestraight line (S2) which runs from the bottom row of bobbins in thebobbin creel (3) via the grid (X) of an existing installation and thenon to the grid (100). For the sake of clarity, the grid (X) does notform part of the installation according to this disclosure and is merelyadded to the figure in order, by comparison with the prior art, to beable to present an effect of the disclosure.

The lines (S1), (S2) show the size of the angles (relative to ahorizontal plane) at which the warp yarns are brought to the grid (X)and then on to the grid (100) according to the prior art, andconsequently the angle which the supplied warp threads then take.

During weaving, the heddles (16), (17) are moved up and down in order toposition the warp threads (11), (12) correctly according to thepredefined weaving pattern. The pull-back springs (18), (19) in theirlowest position provide the necessary downward force for allowing theshed formation to proceed correctly, but must also overcome the upwardlydirected force which is a consequence of the yarn tension.

If the heddle is moved to a higher position for shed formation, thedownward spring force increases proportionally with the upward movementof the heddle in order finally to reach a value which is much greaterthan necessary.

On FIG. 2, for a number of successive weft insertion cycles (the stateof the main shaft of the weaving machine is shown on the horizontal axisin degrees), graph line G1 shows the development of the downward forcewhich the springs (18), (19) exert on the heddle (16), (17) (on the leftvertical axis, in N) of a pile-forming pile warp thread; and graph lineG2 shows the development of the alternating upward and downwardcomponent of the force (in N) which is exerted on the heddle (16), (17)as a result of the yarn tension in the pile-forming pile warp thread.The latter force is referred to in brief below as the “yarn tensioningforce”.

For the sake of clarity, where a force (spring force or yarn tensioningforce) is marked as negative in FIGS. 2 and 3, this means that the forceis pulling the heddle upward. This is clear for example because the yarntensioning force is negative in the graph regions where the heddle is inits lowest position. It is evident that the force exerted by the yarntension on the heddle then has an upwardly directed component whichpulls the heddle upward.

Graph line G4 shows the position of the heddle eye (in mm on thevertical axis on the right-hand side).

Graph line G3 shows the development of the sum of the spring force andthe yarn tensioning force. Here we see two high peaks (P1), (P2) of thistotal force. The graph line G3 shows the forces to which the differentmachine components are subjected. It should be noted that the graphs inFIGS. 2 and 3 show the forces which are the result of movements of asingle pile warp thread, whereas on a typical face-to-face weavingmachine for example, 32,000 pile warp threads or more may be present.

FIG. 3 shows the development of the spring force and the yarn tensioningforce on the heddle of a pile-forming pile warp thread when the yarntension is controlled or steered so as to achieve lower peak values anda lower mean of the sum of the spring force and yarn tensioning force.

Because of this steering or control, also a spring may be used with alower spring constant and a lower spring pretension force (0.15 Nlower)—this is the downwardly directed spring force when the heddle isin its lowest position. The pretension force may be lower because,thanks to the steering or control of the yarn tension, less upward yarntensioning force is exerted by the pile warp thread.

In FIG. 3, the same indications (G1), (G2), (G3) and (G4) are used forthe graph lines as on FIG. 2, with the same meanings: namely thedevelopment of the downward spring force (G1), the development of theyarn tensioning force (G2), the development of the sum of the springforce and the yarn tensioning force (G3), and the position of the heddle(G4). The left vertical axis gives the values of the forces (in N), andthe right vertical axis gives the values of the positions of the heddle(in mm). The horizontal axis gives the state of the main shaft of theweaving machine in degrees.

Graph line (G5)—the dotted line—gives the value of the mean of said sumof the spring force and yarn tensioning force.

It is clear from graph line (G3) that for the total force on the heddle,the high peaks have disappeared (compare with FIG. 2, peaks P1 and P2).In addition, the mean value of this total force is lower. In the designwithout a steering or control system (FIG. 2), the calculated mean ofthis total force is 2.91 N, while in the design with control system,this total force is 2.72 N (graph line G5 on FIG. 3).

These effects mean a lower load on the machine, wherein again it mustnot be forgotten that the values from the graphs show the forces whichare the result of the movements of a single pile warp thread, whereas ona typical face-to-face weaving machine for example, 32,000 pile warpthreads or more may be present.

The advantageous aspects of this disclosure are not restricted to pilewarp threads but also apply to warp threads of another type which arepositioned by the jacquard device, or to single-face weaving machines.

In the claims:
 1. Shed-forming device comprising a jacquard device witha number of heddles, for positioning at least one associated warpthread, wherein each heddle is connected to a pull-back element, forexerting a downward force on the heddle, wherein the shed-forming devicecomprises, per heddle, a yarn tensioning element which is provided tochange the yarn tension in at least one associated warp thread, and thatthe shed-forming device comprises a control or steering unit which isprovided, in cooperation with the respective yarn tensioning elements,for steering or controlling the yarn tension in at least one associatedwarp thread, separately for each heddle, such that the total downwardforce on the heddle, is brought to a specific value or varies accordingto a specific profile.
 2. Shed-forming device according to claim 1,wherein each yarn tensioning element comprises a roller which is drivenby a motor and which is in contact with at least one warp thread, andwhich is intended to rotate in the one or the other direction ofrotation in order to move said warp thread in a direction opposite thefeed direction of the warp threads, or to move the warp thread or tomove with the movement thereof or to facilitate the movement thereof ina direction which is the same as the feed direction of the warp threads,in order to increase or decrease respectively the yarn tension in saidwarp thread.
 3. Shed-forming device according to claim 1, wherein thatparameters of the jacquard device or of a weaving machine cooperatingwith the jacquard device, or data or parameters connected with theweaving pattern, are made available to the control or steering unit inorder to be taken into account in determining the target value for thetotal downward force.
 4. Shed-forming device according to claim 1,wherein it comprises a storage unit in which two or more reference yarntension profiles and/or two or more reference series of at least onereference value for the yarn tension are stored, and that the control orsteering unit is provided to select a reference profile or referenceseries from this collection in order to use these as target value(s) ora succession of target values for steering or control.
 5. Shed-formingdevice according to claim 1, wherein the pull-back elements are springs.